This invention relates to self-extruding fasteners comprising a head provided with means for engaging a rotary tool, a main body formed on its outer surface with two screw threads of the same outside diameter, root diameter and pitch, and a tapering portion disposed opposite the head with respect to the main body and terminating at a sharp pointed forward end.
Self-extruding fasteners of this type have particular utility in fastening two members together, that is, in securing a member, such as a plasterboard, to another member made of a thin sheet of metal, such as a metal stud used as a framework for producing a wall or a ceiling by a dry process. Generally, self-extruding fasteners used for this purpose are required to be able to perform the following functions in an instant in a single operation:
(1) Forming a guide opening in a thin sheet of metal which is one member to which another member is to be fastened;
(2) Extruding forwardly the material of the thin sheet of metal so as to enlarge the guide opening into a cylindrical bore formed in a projection;
(3) Forming an internally threaded portion on the wall of the cylindrical bore formed in this way; and
(4) Clamping the member to be secured to the thin sheet of metal and holding the same in place.
This invention has as its object the provision of a self-extruding fastener comprising a head, a main body and a tapering portion, wherein screw threads of a shape best serving the purpose of performing the aforesaid four different functions are formed on its outer surface.
The aforementioned object of the invention is accomplished by forming on the fastener two screw threads which essentially extend only on the main body, such screw threads having a height which is gradually reduced in a portion where the main body ends and the tapering portion begins, until the two screw threads disappear from the fastener, with a third screw thread being generated in a position midway between the two screw threads and in the portion where the main body ends and the tapering portion begins, the third screw thread gradually increasing its height and extending to a pointed forward end of the tapering portion. In this type of self-extruding fastener, the third screw thread advantageously has its outside diameter and root diameter reduced while having its lead angle increased, as it draws near the pointed forward end of the tapering portion.